The invention relates to a throttle-valve assembly having a housing, which has a continuous throttle opening through which a gaseous medium can flow in a main flow direction, in which a throttle valve fastened pivotably on a throttle-valve shaft is arranged in the throttle opening, in which the throttle-valve shaft can be pivoted by an actuator arranged in the housing, in which, starting from the axis of rotation of the throttle-valve shaft downstream along the main flow direction of the gaseous medium, the throttle opening has an approximately straight cylinder section with a height H1 and a radius RZ and in which a spherical-cap section adjoins the approximately straight cylinder section.
To control the quantity of fresh gas for a motor vehicle, use is generally made of throttle-valve assemblies. Throttle-valve assemblies comprise a housing having a throttle opening and a throttle element arranged in the throttle opening. The throttle element assumes a certain position in the throttle opening to allow through a certain quantity of fresh gas. For this purpose, the throttle element can be activated mechanically or electronically.
Housings of throttle-valve assemblies are generally produced from plastic or metal. Housings of throttle-valve assemblies which are manufactured from metal, for example, aluminum, may have particularly low tolerances. Low tolerances are necessary for a throttle-valve assembly, in the region of the throttle valve, particularly if the intention is for the quantity of flow medium passing through the throttle opening of the throttle-valve assembly to be able to be influenced even by a particularly small movement of the throttle valve. In the closing region of the throttle valve, these requirements are also referred to as leakage-air requirements. However, metal housings of throttle-valve assemblies have the disadvantage that, after the housing has been produced, for example by die-casting, complicated re-machining of the housing is required. For example, re-machining of housings made of aluminum is necessary in order to ensure the functional requirements provided in and on the housing. Functional requirements are, in particular, the flow passage, the holder for the actuator and gear axis spacings. Precise machining of the bearing seats is also usually necessary, since the correct operating play (bearing clearance) is produced only by the press fit on the needle bearing.
Throttle-valve assembly housings manufactured from plastic have a lower weight than throttle-valve assembly housings which are manufactured essentially from metal, in particular aluminum. Furthermore, plastic, as the material, can also be adapted in an especially simple manner to a wide variety of geometric configurations of the housing. Moreover, in the case of plastic housings produced by injection molding, inserts, for example bearings for mounting the throttle-valve shaft, can be placed into the injection mold provided for the housing and encapsulated with plastic.
The throttle opening of a throttle-valve assembly usually has an approximately cylindrical cross section. The approximately cylindrical cross section of the throttle opening has the effect of causing a continuous increase in the quantity of flow medium flowing through over the working range of the throttle valve when the throttle valve is opened. This may prove disadvantageous if the throttle valve and the throttle opening have a particularly large diameter, for example 90 mm or more. This is because, from a certain opening angle of the throttle valve, the mass of flow medium passing through the throttle opening only changes to a particularly small extent per unit of time, in particular at a particularly large diameter of the throttle valve, when the position of the throttle valve changes, which means that a finely graduated control of the power of the motor vehicle is no longer possible from a certain opening angle of the throttle valve.
The invention is therefore based on the object of specifying a throttle-valve assembly of the type mentioned above, which reliably ensures a finely graduated control of the medium passing through the throttle opening during operation of the throttle-valve assembly, in particular for throttle valves having a particularly large diameter.
According to the invention, this object is achieved by virtue of the fact that the spherical-cap section has a central point which, starting from the axis of rotation of the throttle-valve shaft downstream along the main flow direction of the gaseous medium, is displaced by a distance H2, with the spherical-cap section having a radius RK which is approximately determined by the following equation:
RK=[RZ2+(H1xe2x88x92H2)2]1/2.
The invention starts from the consideration that a throttle-valve assembly which reliably ensures a finely graduated control of the medium passing through the throttle opening during operation of the throttle-valve assembly, in particular for throttle valves having a particularly large diameter, is to be manufactured with a particularly low outlay on production. The throttle valve is therefore to remain unchanged in its shape and design in order, for cost reasons, to be able to continue installing standard throttle valves in the throttle-valve assembly. Since the housing of a throttle-valve assembly is usually adapted to specific installation requirements, a finely graduated control of the medium passing through the throttle opening during operation of the throttle-valve assembly is to be reliably ensured by means of a special shaping of the throttle opening. In addition to the simple cylinder shape of the throttle opening, a spherical cap can be impressed in a particularly simple manner into the throttle opening of a throttle-valve assembly. The radius of the spherical cap and distance of the central point of the spherical cap from the central point of the throttle-valve shaft are available in this case as parameters for the design of the spherical cap. Extensive considerations and calculations have led to the surprising result that displacement of the central point of the spherical cap relative to the central point of the throttle-valve shaft linked to a requirement for the radius of the spherical cap has the effect of reliably ensuring a sensitive control of the medium passing through the throttle opening even for throttle valves having a particularly large diameter.
Starting from the axis of rotation of the throttle-valve shaft upstream counter to the main flow direction of the gaseous medium, the throttle opening advantageously has an approximately straight cylinder section with a height G1 and a radius PZ, with a spherical cap section adjoining the approximately straight cylinder section, the spherical-cap section having a central point which, starting from the axis of rotation of the throttle-valve shaft upstream along the main flow direction of the gaseous medium, is displaced by a distance G2, with the spherical-cap section having a radius PK which is approximately determined by the following equation:
PK=[PZ2+(G1xe2x88x92G2)2]1/2.
The characteristic curve along the throttle-valve assembly can additionally be flattened by the fact that the throttle opening has a spherical-cap section both downstream and upstream of the axis of rotation of the throttle-valve shaft, the radius of both spherical caps being spaced apart from the central point of the throttle-valve shaft and the radius of the spherical caps satisfying at least one of the equations stated above.
In an advantageous manner, the value of RZ is equal to the value of PZ and the value of RK is equal to the value of PK. A throttle opening of a throttle-valve assembly, which opening is constructed symmetrically relative to the closed position of the throttle valve, can be produced with particularly little outlay. In this case, the parameters H1, H2 and RZ can be used to adapt the particular throttle-valve assembly to specific requirements of the particular motor vehicle.
The housing is advantageously produced by injection molding and is predominantly made of plastic, with at least the straight cylinder section in the region of movement of the throttle valve being formed by a metal insert injected into the housing. A metal insert for a plastic housing can be manufactured with smaller tolerances than is possible for a housing made of plastic. Therefore, in order to obtain a predetermined characteristic, a throttle opening which is formed from metal stands out. In order, however, at the same time, to ensure a throttle opening having particularly small tolerances and a particularly low weight of the throttle-valve assembly, only the region of the throttle opening relevant to the characteristic curve is manufactured from metal, the remaining region of the housing being made predominantly or completely of plastic.
The spherical-cap section is advantageously formed by a metal insert integrated in the housing. By this means, an individual spherical-cap shape can be realized with a particularly low outlay for each type of throttle-valve assembly.
Both the cylinder section and the spherical-cap section are advantageously formed by a single-piece metal insert. As a result, sealing problems between the approximately straight cylinder section in the region of movement of the throttle valve and the spherical-cap section do not occur. Moreover, unevennesses in the boundary region between the approximately straight cylinder section in the region of movement of the throttle valve and the spherical-cap section could result in swirling of the gaseous medium passing through the throttle opening during operation of the throttle-valve assembly, which could have a negative effect on the characteristic curve of the throttle valve.
The metal insert is advantageously constructed so as to hold the bearings of the throttle-valve shaft. As a result, the bearings are integrated in the mechanical stability of the metal insert. This arrangement of the bearings enables the throttle-valve shaft to be mounted in a particularly stable manner in the metal insert.
A position detection device is advantageously provided for the throttle-valve shaft, a holder being integrated in the metal insert for the position detection device. In this case, the mechanical stability of the metal insert ensures that the position detection device is particularly securely held in the housing of the throttle-valve assembly. At the same time, the position detection device can additionally be pre-adjusted relative to the throttle-valve shaft via the holder provided in the metal insert, as a result of which the position detection device requires only a particularly small amount of adjustment. In this case, the position detection device can be put into place even at the point at which the metal insert is integrated in the housing.
The actuator is advantageously to be arranged on a base plate, the base plate being constructed as a single piece with the metal insert. By this means, heat arising during operation of the actuator can be conducted away to the metal insert via the base plate, with sufficient cooling of the metal insert being reliably ensured by the gaseous medium passing through the throttle opening.
The advantages obtained with the invention reside, in particular, in the fact that a characteristic curve for a throttle-valve assembly can be obtained by a special shaping of the throttle opening in the region of movement of the throttle valve and not by a change in the shape of the throttle valve and/or arrangement of the throttle-valve shaft, said characteristic curve covering a range which has previously not been achieved with known throttle-valve assemblies. This range of the characteristic curves for a throttle-valve assembly that has been acquired by the invention is advantageous in particular in the case of throttle valves having a particularly large diameter, so that the latter, in spite of their size, reliably ensure a particularly finely graduated control of the power of the internal combustion engine.